python-manhole

Manhole is in-process service that will accept unix domain socket connections and present the stacktraces for all threads and an interactive prompt. It can either work as a python daemon thread waiting for connections at all times or a signal handler (stopping your application and waiting for a connection).

Access to the socket is restricted to the application's effective user id or root.

This is just like Twisted's manhole. It's simpler (no dependencies), it only runs on Unix domain sockets (in contrast to Twisted's manhole which can run on telnet or ssh) and it integrates well with various types of applications.

Documentation:	http://python-manhole.readthedocs.org/en/latest/

Usage

Install it:

pip install manhole

You can put this in your django settings, wsgi app file, some module that's always imported early etc:

import manhole
manhole.install() # this will start the daemon thread

# and now you start your app, eg: server.serve_forever()

Now in a shell you can do either of these:

netcat -U /tmp/manhole-1234
socat - unix-connect:/tmp/manhole-1234
socat readline unix-connect:/tmp/manhole-1234

Socat with readline is best (history, editing etc).

Sample output:

$ nc -U /tmp/manhole-1234

Python 2.7.3 (default, Apr 10 2013, 06:20:15)
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>> dir()
['__builtins__', 'dump_stacktraces', 'os', 'socket', 'sys', 'traceback']
>>> print 'foobar'
foobar

Features

• Uses unix domain sockets, only root or same effective user can connect.
• Can run the connection in a thread or in a signal handler (see oneshot_on option).
• Can start the thread listening for connections from a signal handler (see activate_on option)
• Compatible with apps that fork, reinstalls the Manhole thread after fork - had to monkeypatch os.fork/os.forkpty for this.
• Compatible with gevent and eventlet with some limitations - you need to either:
  • Use oneshot_on, or
  • Disable thread monkeypatching (eg: gevent.monkey.patch_all(thread=False), eventlet.monkey_patch(thread=False)
• The thread is compatible with apps that use signalfd (will mask all signals for the Manhole threads).

Options

manhole.install(
    verbose=True, patch_fork=True, activate_on=None, oneshot_on=None,
    sigmask=manhole.ALL_SIGNALS, socket_path=None, reinstall_delay=0.5,
    locals=None)

• verbose - set it to False to squelch the stderr ouput
• patch_fork - set it to False if you don't want your os.fork and os.forkpy monkeypatched
• activate_on - set to "USR1", "USR2" or some other signal name, or a number if you want the Manhole thread to start when this signal is sent. This is desireable in case you don't want the thread active all the time.
• oneshot_on - set to "USR1", "USR2" or some other signal name, or a number if you want the Manhole to listen for connection in the signal handler. This is desireable in case you don't want threads at all.
• sigmask - will set the signal mask to the given list (using signalfd.sigprocmask). No action is done if signalfd is not importable. NOTE: This is done so that the Manhole thread doesn't steal any signals; Normally that is fine cause Python will force all the signal handling to be run in the main thread but signalfd doesn't.
• socket_path - Use a specifc path for the unix domain socket (instead of /tmp/manhole-<pid>). This disables patch_fork as children cannot resuse the same path.
• reinstall_delay - Delay the unix domain socket creation reinstall_delay seconds. This alleviates cleanup failures when using fork+exec patterns.
• locals - Names to add to manhole interactive shell locals.
• daemon_connection - The connection thread is daemonic (dies on app exit). Default: False.
• redirect_stderr - Redirect output from stderr to manhole console. Default: True.

What happens when you actually connect to the socket

1. Credentials are checked (if it's same user or root)
2. sys.__std*__/sys.std* are be redirected to the UDS
3. Stacktraces for each thread are written to the UDS
4. REPL is started so you can fiddle with the process

Known issues

SIGTERM and socket cleanup

By default Python doesn't call the atexit callbacks with the default SIGTERM handling. This makes manhole leave stray socket files around. If this is undesirable you should install a custom SIGTERM handler so atexit is properly invoked. Example:

import signal
import sys

def handle_sigterm(signo, frame):
    sys.exit(128 + signo)  # this will raise SystemExit and cause atexit to be called

signal.signal(signal.SIGTERM, handle_sigterm)

Requirements

OS:	Linux, OS X
Runtime:	Python 2.6, 2.7, 3.2, 3.3, 3.4 or PyPy

Similar projects

• Twisted's old manhole and the newer implementation (colors, serverside history).
• wsgi-shell - spawns a thread.
• pyrasite - uses gdb to inject code.
• pydbattach - uses gdb to inject code.
• pystuck - very similar, uses rpyc for communication.
• pyringe - uses gdb to inject code, more reliable, but relies on dbg python builds unfortunatelly.
• pdb-clone - uses gdb to inject code, with a different strategy.